At the IGAC/SPARC
Chemistry-Climate Model Workshop held in Davos in May 2012
four expert teams have been formed to foster collaborations between
modelers and
observationalists for an improved model evaluation. Several activities
are currently underway that aim at a better access and
comparability to observations. This website provides links to some of
the ongoing activities.

For further
information, please also see the CCMI simulation document available here.

This expert group provides the link between
instrument
teams (primarily via the SPARC Data Initiative) and CCMI with the goal
to
improve the comparability between models and limb-viewing satellite
observations from the upper troposphere to the lower mesosphere. Key
issues of
model-measurement comparisons in this region are 1) knowledge of the
quality of
the available data sets for particular evaluations and 2) the impact of
different sampling patterns on the representativeness of the data sets,
which
is especially important for trace gas species with strong diurnal
cycles. The
expert group will provide guidance on these issues based on the results
of the
SPARC Data Initiative. This international team effort is currently
carrying out
a comprehensive inter-comparison of vertically-resolved monthly zonal
mean
trace gas climatologies derived from most available stratospheric limb
satellite measurements with the goal to gain better knowledge of the
uncertainty and limitations of the different data sets. A list of zonal
monthly
mean climatologies (which will be directly comparable to model T2M
fields and
will be made publicly available by autumn 2013) can be found in Table
S3 of the
CCMI document. Along with the climatologies, the sampling patterns of
the
different satellite instruments will be provided. The latter can be
used to
sub-sample model fields in order to account for diurnal sampling issues
affecting the zonal mean climatologies of shorter-lived species. The
team will
help to extend currently available satellite databases by additional
parameters, classes of data sets (e.g., single profile information) and
satellite instruments, and will provide updated stratospheric tracer
diagnostics for implementation into the NCAR-Diagnostic Tool or via the
obs4MIP
data base (TBD). An extension of the SPARC Data Initiative into the
upper
troposphere and lower mesosphere covering aspects of 3D and
shorter-term
availability is in its planning phase.(More details on the Initiative
can be
found at the SPARC
Data Initiative website.

There is
now a wealth of satellite data with which to evaluate processes and
trace gas
distributions within models. Each of these datasets has its own
strengths/limitations and often provides complementary information to
other datasets.
A proper comparison between satellite observations and models requires
sampling
the model output at the times and locations of the measurements and
interpolating the model data to the observed vertical levels.
Comparisons to
satellite data should in addition consider a priori profiles and
averaging
kernels from the retrievals when sampling model output to, for example,
calculate tropospheric columns for trace gas species. During the last
few
years, several satellite simulators have been developed which either
involve
on-line calculations or post-processing to provide model output more
directly
comparable to remote sensing observations from satellites. Several
models now
have the capability to sample model output along sun-synchronous
satellite orbits
(see for example the SORBIT routine in Jöckel et al. (2010)). To
facilitate and
encourage a proper comparison to satellite data, we therefore provide
local
times and measured species for some remote sensing products that could
potentially be used for evaluating trace gases, see Tables S1 in
the CCMI simulation document which is
available here.

A document
describing the availability of ground based measurements and
suggestions for
comparisons to ground-based datais available here.
These comparisons are possible with
the standard monthly output generated using CMOR tables.

The website of the CCMI
insitu aircraft measurement expert group can be found here. This
website includes a collection of campaigns, flightpath data, and
observational data that can be used for the evaluation of CCMs.

Comparisons
to more local measurements made for example during in-situ aircraft
campaigns
exhibit the problem of a mismatch of spatial and temporal scales
between
observations and models. CCMs and ESMs usually run at horizontal
resolutions of
a few hundred kilometers, whereas field experiments sample local air
masses.
Similar to sampling model output along sun-synchronous satellite
orbits,
several models now have the capability to interpolate the model data to
the
flight path during the model simulation (see for example the S4D
routine in
Jöckel et al. (2010)). This comparison is very useful in
particular for the
REF-C1SD simulation, which has specified dynamics matching the
meteorological
situation of particular years and thus allows a more direct comparison.
To
facilitate this comparison, we provide the flight paths of several
aircraft
campaigns at the CCMI website in NASA AMES format. Here we will provide
links to flight path and obeservationl data that can be used for model
evaluation. Updates
will be made available on this website.
The charge of the expert team on insitu
aircraft measurements will be to identify methodology to
meaningfully evaluate CCM simulations against in-situ observations via
analyses
that bridge the disparate temporal and spatial scales.Following the successful CCMVal exercise,
carry out observation/model comparisons by improving access to vetted
in-situ
data sets to facilitate validation of model input inventories, to
assess simulations
of atmospheric processes, and to evaluate simulations of longer-term
trends.